1. Field of the Invention
The present invention relates to a body fluid absorbing article such as a sanitary napkin or a paper diaper for absorbing and holding a body fluid and, more particularly, to a body fluid absorbing article having a laminated absorbing structure, which is improved in the spot absorptivity and in the diffusivity in an absorbent, and which is improved in the characteristics of a body fluid migration to the absorbent.
2. Description of the Related Art
As this body fluid absorbing article having the laminated absorbing structure, there is known in the prior art a two-layered structure, as disclosed in JP-A-2001-170111, or a three-layered structure, as disclosed in JP-T-8-503397. The former is cubically bulged by forming an upper layer smaller than a lower layer in the portion of the sanitary napkin to be brought into abutment against the discharge portion of a human body. The latter is provided with three-layer absorbent whose each layer is dense over substantially whole area and is enabled to hold the satisfactory characteristics of the material for sucking the fluid even if the discharge quantity increases.
Generally, the absorbent used in the body fluid absorbing article of this kind is characterized by causing the body fluid to permeate the more quickly for the lower density and the more slowly for the higher density but by holding the body fluid the more easily. The present invention has been conceived by making skillful use of those characteristics. On the contrary, the aforementioned body fluid absorbing article of the prior art has disclosed the laminar structure for the absorbent but has failed to make the layers different in density. Without this view point, moreover, the existing body fluid absorbing article is not excellent in both the spot absorptivity and the body fluid diffusivity.
In the prior art, moreover, it has been disclosed in JP-A-57-205503 or JP-A-64-45801, for example, that the body fluid treating characteristics in the absorbent, that is, the absorptivity and the diffusivity are adjusted to block the flow of the body fluid thereby to prevent the leakage by embossing the absorbent of the body fluid absorbing article.
With the absorbent being thus embossed, the indented portions take a high density, and the remaining portions take a low density. These indented portions (or the higher density portions) and the remaining portions (or the lower density portions) are not in the laminated relation in the thickness direction of the absorbent. No matter how the density might be adjusted, therefore, the absorbing mode can neither absorb the body fluid quickly nor then diffuse it. As a result, the body fluid hardly permeates, and the higher density portions of a high body fluid absorbing and retaining properties come into contact with the surface layer to contact with the skin. Thus, there arise problems that the body fluid flows back (as called the “wet back”), and that the wearer feels a sticky feel. Especially when the indented portions are formed by the embossing treatment or the like on the surface layer side of the absorbent, there arises a problem that the migration of the body fluid to the absorbent is insufficient.
As a countermeasure for preventing a sideway leakage in the body fluid absorbing article, moreover, there is also known a method of increasing the liquid distribution in the longitudinal direction by indenting the absorbing structure from the surface to the back and by forming longitudinally extending indented lines in the two side portions of the body fluid absorbing article. Much body fluid is held in the high density portions to abut against the skin so that the problem of the back flow or the sticky feel becomes more serious than the of the case of JP-A-57-205503 or JP-A-64-45801. Moreover, these methods still have problems that the absorbent structure becomes hard to give an uncomfortable feel to the wearer, and that the cushioning properties are lost to establish a clearance between the absorbing structure and the body of the wearer.
In the body fluid absorbing article of the prior art, as described hereinbefore, the spot absorptivity, i.e., the ability to receive the body fluid quickly in the absorbent, and the diffusivity, i.e., the ability to diffuse the body fluid throughout the inside of the absorbent cannot be said sufficient in the least, although they are extremely important factors from the viewpoints of the using feel and the leakage prevention.